Recovery of tin and similar metals



Aug. 15, 1944.

T. W. BENSON ETAL RECOVERY 0F TIN AND SIMILAR METALS Filed Oct. 8, 19402 Sheets-Sheet l ATT RNEY INVENTORS Thoma/s Il( .Benspn/ Bfem/fam 17H0finan,

mw Kw Al1g- 15, 1944 T. w. BENSON ETAL 2,355,777

RECOVERY OF TIN AND SMILAR METALS Filed oct. 8, 1940 2 sheets-sheet 2INVENTORS Themas Itenson/ to recover these .alkali solutions.

Patented Aug. l5, 1944 RECOVERY F TIN. AND SIMILAR METALS Thomas W.Benson and Bertram F. Hoifman, A Philadelphia, Pa.

Application October 8, 1940, Serial No. 360,280 8 Claims. (CL 23--144)'I'he present invention relates to a method of recovering tin andsimilar metals from scrap containing the same.

Although the present invention will be particularly described in itsapplication to the recovery of tin from tin plate scrap, such as usedtin cans, it is to be understood that it has a broader application tothe recovery of lead, tin, aluminum, chromium, vanadium, tungsten andsimilar amphoteric metals from scrap or waste material containing thesame, particularly where such waste material is principally composed ofa relatively less costly metal, as for example, steel or iron.

It has not been found most satisfactory to recover tin from tin scrap orwaste tin plate byv treatment with acid or by treatment with halo` gens,sincethey will often result in the production of a relatively impure tinand give low yields.

It also has not been found most satisfactory metals by hot or boilingaqueous It is among the objects of the present invention to provide animproved process of recovering tin or similar metals from scrap con- Thesolubilizing reagent then is caused to thoroughly coat itself over thescrap, while the water is removed and evaporated, with the result thatthe solubiliz'ing reagent or caustic alkali will be caused to fuse orilow over the scrap in moisture reduced or dehydrated condition. 'I'hiswill just give enoughchemicals to convert all of the tinto stannate andwill result in a complete combination of the tin or other metal to berecovered with the caustic alkali to form an alkali metal salt.

This alkali metal salt then may be readily recovered and the metal oxideor hydroxide may be taining the same, and particularly from iron or lsteel scrap containing the same, particularly where the tin or otheralkali reactive metals are .in the form of surfacings, coatings orplatings upon relatively less costly metal, such as, for ex-.

ample, iron or steel.

It is a further object to recover tin and similar metals from scrap.such as tin cans or tin plate containing the same, in which the tin willbe recovered at low cost and vin a relatively high state of purity.

Still further objects and pear in the more detailed description setforth below, it being understood, however, that this more detaileddescription is given by way of illustration and explanation only, andnot by way of limitation, since various changes therein may be made bying from vention.

In accomplishing the above objects, it has been found mostsatisfactoryaccording to one embodiment of the present invention to first apply thesolubilizing reagent, such as a caustic alkali, together with anoxidizing agent, such as sodium nitrate, sodium chlorate, or sodiumbichromate, to the scrap after the scrap has been cleaned, degreased andbroken up, said caustic alkali and oxidizingagent being in an aqueoussolution or in nuid form.

the scope and spirit ofthe present inadvantages will ap-y those skilledin the art without depart- 1 obtained from the salt solution, ifdesired, by precipitation, as for example, with carbon dioxide,following which the tin oxide or other amphoteric metal oxide may beobtained in pure form by heating or calcination. y

The scrap, on the other hand, from which the tin or other amphotericmaterial has been removed, may be washed and lutilized as scrap metal.Referring to the drawings, which show one embodiment, according to thepresent invention,

tration and'not limitation,

Fig. 1 is a diagrammatic ow sheet illustrating the recovery of the tinor other similar metal andthe various equipment which may be utilizedfor this purpose;

Fig. 2 is a diagrammatic showing of the fusion furnace device of Fig. 1,upon an enlarged scale as compared to Fig. 1;

Fig. 3 is a transverse sectional view of the furnace of Fig. 2; and

, Fig. 4 is a diagrammatic showing of analternative furnace devicesimilar to Fig. 2.

Referring to the drawings, the scrap is prepared for treatment bymacerating the cans in the macerator I0. The rolls II `of maceratororshredding machine I0 may split them to any convenient width,` say to 2inch widths.

After the scrap passes the macerating wheels II, it passes into thechute I2 and then into the washer I3. In`the washer I3, the shreddedscrap is immersed or' washed in hot Water containing a detergent orcaustic solvent, if desirable.

The washer tank I3 has a belt I 4, which'elevates the scrap, asindicated at I5, to dump it into the rinsing tank I6.

In the rinsing tank I6 the scrap is washed p free of the detergent orcaustic solvent and thoroughly degreased and the scrap is4 picked up bythe belt II and then dumped into the conditioning tank I8.

In the conditioning tank I8 the scrap maybe 4has a rotating tube 21 .ingat 42 supported on teeth 31, which mesh, with the worm tin scrap withini spraying with the correct amount of immersed in a conditioningvsolution consisting of a 35 to 65% caustic alkali solution, such ascaustic soda, containing from to 20% of sodium nitrate.

This caustic soda is preferably first dissolved in approximately anequal weight of water and is kept at a temperature of 120 to 160 F. andthen the sodium nitrate is added. The concentration of the solution ispreferably so regulated that approximately 5% by weight of the causticsoda composition will cling or attach itself to the scrap upon removalfrom the conditioning tank I .3.

It will be noted that both the washing tank i3; as well as theconditioning tank I9, are provided with heating devices indicateddiagrammatically at I9 and 20 to maintain a desired temperature.

The conditioning tank I9 is supplied with the caustic alkali solutionfrom the make-up tank 2i through the conduit 22.- The scrap in theconditioning tank I9 istaken up by the moving belt 23, which has anelevated portion 24, which will dump the scrap into the receiving spout25 of the fusion furnace 28.

The fusion furnace, as shown best in Fig. 2, provided with the collars29. and 39.

The collar 29 rests upon portion 30 of the roller 3l, mounted at 32 inthe support of the furnace 35. roller 45, turning on the shaft 4i havinga bearthe wall 43 of the furnace 35. The other collar 29 is providedwith gear drive 33,

the reduced diameter which is rotatably 33 on the wall 34 which drivesthe rotating tube 21.

It will be noted that as shown in cross section in Fig. 3, the tube 21is positioned in the upper curved portion 44 of the furnace 35, whichhas the front'wall 45 and the rear wall 49, which rear wall 45 receivesthe oil burners 39.

The upper portion 41 of the wall of the furnace is projected forwardlyto force the gases to pass along the path indicated by the arrows 48before passing out through the stack 49.

Travelling through the tube 21 are a series of plates 50, which areconnected together by the linked chain 5| and which are -propelled bythe toothed wheels 52 and 53 rotating in the direction 54. These wheelsare provided with the shafts 55 and 55 and their teeth 52 have flatsides.51 and 59 to pick up and advance the plates I9 in the mannerindicated, whereby the vmaterial'is kept moving in the direction 59through the tube 21. K

At `the same time, tube 21 is rotated to give a uniform coating orsurfacing of the caustic material.

Preferably the temperature in the rotating tube 21 is maintained atabout 350 to 400 F, and and air is desirably excluded from the interiorof the tube as much as possible. a

If desired, an inert atmosphere should be caused to flow through therotating tube 21, together with the scrap. The timeA oi' treatment ofthe the rotating tube 21 should -be sufficient to fuse the causticalkali onto the surface of the scrap and cause the conversion of the tininto sodium stannate. A continuous rotation assures an even distributionof the caustic alkali and the sodium stannate and a uniform heating ofthe mass in the tube to a temperature of about soo @500 c.

`Thecoating of the tin scrap by immersion or 'Ihe collar 39 rides uponthe impurities, such as any iron particles alkaline potassium or sodiumcompounds to complete the formation of the sodium stannate in theabsence of a non-oxidizing atmosphere, together with the agitation orlrotating of the scrap while evaporating the moisture and melting thecaustic a1- kali and alkali metal salts to assure even and completedistribution and even heating and complete reaction is a most importantfeature of the present invention and results in the recovery of tin ofhigh purity and at minimum cost.

It is desirable that a substantial amount of water be driven off duringthe passage through the tube 21, which also aids in displacing the air,and that the caustic alkali or alkali metal salts fuse and form a syrupysolution which thoroughly coats the tin scrap and dissolves or takes upthe tin surfacing, coating or plating.

The scrap is then discharged while still hot into a tank 30 of hot orboiling. water, where the sodium stannate will dissolve away from theresidual scrap, leaving the sheet iron free of tin. The belt 6| willpick up the scrap and elevate it at 82 to dump it into a second rinsingtank 53. The moving belt- 54 will pick up the scrap and elevate it at65,/ dumping it into the steel scrap storage at 5B. The water in thetank 50 will be kept boiling by the heat of the scrap while the water intank 63 is maintained duite hot. The rinsing water enters the tank 53 at95 and passes from tank 63 to tank BD by the conduit 95, flowingcountercurrent to the scrap.

From the steel scrap storage at 99, the scrap metal may be dumped outthrough the spout 51 into the baler 63, where it may be passed, asindicated by the arrow 69, to a suitable storage and sold as mild steelscrap.

'Ihe solution of sodium stannate, which is produced in the tank 69,should be regulated so that it contains about 12% of dissolved sodiumstannate before it is withdrawn by the conduit 10 to the settling tank1|.

In the settling tank 1I, the solution is permitted to stand to permitsedimentation of any which are discharged through the tank, the solutionisboiled by the steam coil I9 to precipitate the lead plumbate which isinsoluble in hot solution; the precipitated plumbate is also removedthrough the spout 12.

The clarified solution conduit 13 into the tank 14, where it may beevaporated to concentrate the same and to precipitate the sodium.stannate, by a steam coil supplied from the boiler 19 by the conduit9|. The precipiated sodium Stannate may then be passed by the conduit 15to the precipitation tank 16, to which tank Water is added at 92 fordilution and to the bottom of which CO2 is fed at 93 by the conduit 11from theI stack 13- of the' boiler 19. The dilution aids in' causingsolution of sodium carbonate formed. The steam from the boiler 19 isalso fed to the coils I6, i9 and 80.

The carbon dioxide which passes up through the body of liquid in thetank 19-will *result in precipitation of stannic hydroxide which is thencollected and passed through the conduit 9| to the ignition pan 32, andthen to the furnace 33 and improver 94 to form tin metal which isremoved at 94. The oil burner 95 which is supplied with steam from theboiler 19 reduces the tin from the Oxide and the waste gases are usedfor keeping the tinin the improver 94- in molten condition to remove thegranular structure.

During this procedure, howeventhe stannic spout 12. W

hileinthis' then passes through the instead of being Wasted,

-ot the treated scrap and also keeps cover platings, coatings hydroxidemay be taken oi at 85 and treated with acids, such as hydrochloric acidor sulphuric acid, to form tin salts or calcined ignited stannic oxidemight be removed at 86. If desired to produce an alkali-free oxide, thetin hydroxide might also be removed at the point 85,- acidulated withhydrochloric acid to just render the solution acid, and thenreprecipitated by sodium sulphate with boiling to obtain pure tinhydroxide, which may then be calcined to form an alkali-free oxide.

-The residual solution produced inthe tank 18 is wasted but the residualsolution produced in the tank 14 is concentrated in the tank '81 ,by thesteam coil and then returned at 88 to the make-up tank 2|, where nitrecake (NaNOa) is added to produce proper proportions of sodium hydroxideand nitrate for further treatment of scrap. The nitrate helps oxidizethe tin and aids the solvent action of the hydroxide.

The sodium bicarbonate formed in the tank 16,

oil CO2 which may be recovered to treat additional quantities of sodiumstannate solution. The residual dissolved sodium carbonate may beconverted by line to caustic soda, which can be introduced into themake-up tank 2| and then through the conduit 22 into the conditioningtank I8.

In producing metallic tinin .thefurnace and4 improver 83 and 94, thehydroxide may rst be calcined to a. red heat, ,then mixed withsufficient powdered carbon ferric oxide and silica to form a bi-silicateslag, following which the mass may be reduced in the crucible 83 byAbringing it slowly up to slag-forming temperatures. After reduction,the metallic tin may be de-grained in the improver 94 and cast intobars.

When both lead and tin are `present'in the coating or surfacing to beremoved, itmay be desirable to cool the scrap after it passes out of therotating tube 21 and then to immerse'it in warm water of about 130 F.,as contrasted to boiling water.

By this treatment, the iron which may then be ltered or decanted andbrought to a boil for a short period to precipitate the lead. Then theresidual solution may be ltered away from the precipi forms of screwfeed or spiral fins 91 through the rotating' tube 2|, as shown in Fig. 4(similarly functioning parts to those in Fig. 2 being indicated by thesame numerals primed). The spiral fins or screw feed 91 prevent theconditioned tin scrap from passing straight through the tube 21 andcause it to stay in the cylinder sumciently long to be thoroughlytreated. 'I'he terminal ring 98 prevents too rapid discharge the Isodiumstannate liquor in the cylinder 21. It is also possible. to utilizethe,prejsent procedure to reor surfacings of chroand similar. metals.-

as indicated in the tank mium, lead, aluminum The hot dip rinsing,

may be treated to drive thin molten Il, is particularhr of value in thatit will assure."

complete removal of the pounds.

It `will be noted that the caustic soda and CO2 may be readily recoveredand re-used and that there is a substantially complete recovery of thetin. By the present process as much as 70% of the reacting chemicals maybe recovered.

It is thus apparent that the applicant has produced a simple,inexpensive procedure for recovering tin and similar metals from scrapcontaining the same, which can be used most economically with littleconsumption of valuable chemicals.

Many other changes could be effected in the particular features of themethod disclosed, and in specific details thereof, without substantiallydeparting from the invention intended to be defined in the claims, thespecific description herein merely serving to illustrate certainelements by which, in one embodiment, the spirit ofthe invention may beeectuated.

What is claimed is:

1` A process of recovering tin from scrap containing the same, whichcomprises thinly coating a caustic alkali upon such tin scrap and fusingsuchcaustic alkali coating upon the surface of such tin scrap to convertthe tin into' an alkali metal stannate.

2. A method of recovering tin` materials from various sodiumcomdegreased iron or steel scrap containing the same,-

ing away the alkaline tin salts 'that are formed.

recovering tin from tin scrap, which comprises macerating tin scrap,washing the tin scrap, applying a solution of caustic soda and sodiumnitrate to the tin scrap to form a coating thereon, placing the tinscrap in a revolving tube While subjectingl it to a temperature of 300to 400 C. inthe absence 3. A process of of air until all of the tin hasbeen converted into sodium stannate, rinsing the treated tin scrap toremove the sodium stannate, evaporating the rinsing solution toconcentrateit and recover sodium stannate and caustic alkali, blowingcarbon dioxide through an aqueoussolution of said sodium stannate toprecipitate tin hydroxide and recovering the caustic alkali bytreatmentwithy vheating to an elevated temperature to convert the tin into sodiumstannate while agitating the tin scrap.

6. A process of recovering tin from tin` scrap. which comprisesimmersing the scrap into a hydroxide solution, placing the tin scrap ina rotating chamber and heating it toA between 300 to. 400 C. toevaporate the wat r and to form a thin fused sodium hydroxide coatingthereon and .to cause conversion ofthe kali until the tin has beenconverted into'sodium A tin sait, and then washing otl'/ the sodium tinsalt andpexcess caustic alkali.

8. A process of recovering tin from tin scrap .which comprises treatingscrap with a relatively thin molten coating containing an excess of acaustic alkali and an alkali metal nitrate in the I absence of air. v

THOMAS W. BENSON. BERTRAM F. HOFFMAN.

